The present invention relates generally to ink jet printers including printheads and, more particularly, to a ventable ink jet printhead capping and priming assembly that has an open position for relieving defect causing printhead capping pressures that build up when each such printhead is capped, and a closed position that allows for sealed priming of the printhead during periodic maintenance of the printhead.
An ink jet printer of the so-called "drop-on-demand" type has at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink may be contained in a plurality of channels and energy pulses are used to cause the droplets of ink to be expelled, as required, from orifices at the ends of the channels.
In a thermal ink jet printer, the energy pulses are usually produced by resistors, each located in a respective one of the channels, which are individually addressable by current pulses to heat and vaporize ink in the channels. As a vapor bubble grows in any one of the channels, ink bulges from the channel orifice or nozzle until the current pulse has ceased and the bubble begins to collapse. At that stage, the ink within the channel retracts and separates from the bulging ink which forms a droplet moving in a direction away from the channel and towards a recording medium. The channel is then refilled by capillary action, drawing ink from a supply container.
One particular example of a type of thermal ink jet printer is described in U.S. Pat. No. 4,638,337. That printer is of the carriage type and has a plurality of printheads, each with its own ink supply cartridge, mounted on a reciprocating carriage. The channel orifices in each printhead are aligned perpendicular to the line of movement of the carriage and a swath of information is printed on the stationary recording medium as the carriage is moved in one direction. The recording medium is then stepped, perpendicular to the line of carriage movement, by a distance equal to the width of the printed swath and the carriage is then moved in the reverse direction to print another swath of information.
It has been recognized that there is a need to maintain the ink ejecting orifices or nozzles of an ink jet printer, for example, by periodically cleaning the orifices when the printer is in use, and/or by capping the printhead when the printer is out of use or is idle for extended periods. The capping of the printhead is intended to prevent the ink in the printhead from drying out. There is also a need to prime a printhead before use, to ensure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles. Maintenance and/or priming stations for the printheads of various types of ink jet printers are described in, for example, U.S. Pat. Nos. 4,855,764 and 4,863,717, and the removal of gas from the ink reservoir of a printhead during printing is described in U.S. Pat. No. 4,679,059. All of these patents are hereby incorporated by reference.
A continuing problem with prior art capping mechanisms or assemblies is the slow build up of positive pressure within the sealed capping assembly during idle periods of the printer (with the printhead capped). Such positive pressure ordinarily and usually causes air and ink within the printhead orifices or nozzles to be pushed back into the printhead channels feeding the nozzles. This of course results undesirably in subsequent printhead priming difficulties, and print quality defects. This problem is further complicated by the need to have the capping assembly or mechanism be unvented and completely sealed during priming operations of the maintenance periods.
There is therefore a need for a ventable capping and priming assembly that can relieve defect causing printhead capping pressures that build up when each such printhead is capped, and that yet allows for sealed priming during periodic maintenance procedures.